Lithium is an excellent reducing agent capable of reducing most electrolyte solvents. Accordingly, it is extremely useful in high energy density cells. In particular, lithium anodes have increasingly been employed in small primary cells called "button cells" due to their high volumetric energy densities.
Scores of electrochemical lithium systems have been proposed. For button cell applications, it has been the practice to employ nonaqueous systems employing a lithium anode, an electrolytic solution of a solute and solvent, a cathode, and a separator disposed between the anode and cathode. The entire assembly is, of course, enclosed in a can and cover comprising the "button". For a list of lithium cell components see U.S. Pat. Nos. 4,223,079, 4,288,505 and 4,129,686.
Lithium cells are normally sealed with a polymeric insulating grommet disposed at the interface formed by the can and cover. Traditionally, polypropylene grommets which are inert in the presence of the various electrolytes have been used. See U.S. Pat. Nos. 3,990,918 and 4,292,382.
Unfortunately, sealing lithium cells with polymeric grommets requires the parts to mate together perfectly if a non-leaking closure is to be established. As anyone involved with mass production techniques knows, the vagaries of the production line makes such an accomplishment extremely difficult to obtain. U.S. Pat. No. 3,990,918, listed above, attempts to solve this problem by the utilization of a plastic grommet combined with an elastomeric seal. Another method is the application of bitumin to the grommet.
The importance of a good seal cannot be overemphasized inasmuch as the cell must be protected from: (1) drying out and (2) the introduction of moisture into the cell. Lithium and water, when in contact with one another, violently react creating a dangerous condition which cannot be tolerated in a button cell. Accordingly, it is desirable to develop a simple and convenient lithium cell seal and method of applying it.